1. Field of the Invention
The present invention relates to a semiconductor memory technology and, more particularly, to a semiconductor device such as a ferroelectric memory (FeRAM) device and a method for manufacturing the same.
2. Description of Related Art
Ferroelectric random access memory (FeRAM) devices are memory devices using the orientation of an electric dipole induced by a high-frequency alternating current (AC) field. FeRAM devices have a capacitor made of a ferroelectric substance where two poles, established by applying electricity, remain even when the electricity is cut off. Generally, ferroelectric substances are, for example, Pb(ZrxTi1-x)O3 (hereinafter referred to as “PZT”) and SrBi2Ta2O9 (hereinafter referred to as “SBT”).
In recent years, many efforts have been made to decrease the number of mask layers in forming high-capacitance FeRAM devices to enhance price competitiveness. FIG. 1 illustrates an FeRAM where a direct cell contact is formed between a plate line interconnecting capacitors and a top electrode of a capacitor to decrease the number of mask layers.
As illustrated in FIG. 1, an oxygen barrier layer 13, a bottom electrode 15, a ferroelectric layer 17, and a top electrode 19 are sequentially stacked on a first insulation layer 11 formed on a substrate 10 to constitute a capacitor. A shield layer 21 is formed on the capacitor. Since the shield layer 21 prevents other materials from penetrating the capacitor, the characteristics of the capacitor are not degraded. A second insulation layer 27 is formed on the shield layer 21. Another shield layer 23 and another insulation layer 24 may be formed on the second insulation layer 27. A portion of the second insulation layer 27 is removed to expose a part of the top electrode 19 of the capacitor, thereby forming a direct cell contact hole. The direct cell contact hole is formed by additionally removing a portion of the shield layer 21, formed on the top electrode 19, at the same time. Although not shown in the figure, a titanium nitride (TiN) layer is formed as a diffusion barrier and a metal such as, for example, tungsten (W) is deposited and an etch-back process is carried out to form a contact plug 29. A metal is deposited and patterned to form a plate line 25 interconnecting top electrodes of ferroelectric capacitors.
As described above, a shield layer formed to shield a capacitor structure is partially removed when a direct cell contact is formed. Accordingly, there is a region of direct contact between the direct cell contact and the top electrode. In order to complement the direct contact region, a titanium nitride layer is generally formed as a diffusion barrier. However, titanium nitride has poor characteristics as a diffusion barrier for aluminum, which is used in the formation of a plate line. Moreover, nitrogen produced in the process of forming the contact plug or the plate line may diffuse into the ferroelectric substance through the direct contact region and degrade the capacitor.
Embodiments of the invention address these and other disadvantages of the conventional art.